Transceivers of communication systems typically include base-band amplifiers and filters. The base-band amplifiers and filters amplify and filter communication signals before or after transmission. The performance required by the amplifiers and filters is generally determined by the type of wireless communication being supported by the transceivers.
FIG. 1 shows a general prior art receiver chain of a wireless transceiver. An equivalent transmitter chain typically requires equivalent components as the receiver chain. The receiver chain includes an antenna 110, an LNA (low noise amplifier) 120, a frequency mixer 130 an associated LO (local oscillator) signal, a base-band filter 140 and a VGA (variable gain amplifier) 150. As previously stated, the performance required of the receiver chain components is typically determined by the type of wireless communication of the transceiver.
UWB (ultra wide-band) is an evolving wireless communication standard. The Federal Communications Committee (FCC) has mandated that UWB radio transmission can legally operate in the frequency range of 3.1 GHz to 10.6 GHz, at a transmission power of −41.25 dBm/MHz, having a minimum bandwidth of 528 MHz. Basically, UWB devices provide wide bandwidth transmission at very low signal power levels.
The base-band filter 140 of a UWB transceiver should support, for example, a pass-band of over 528 MHz. Additionally, the base-band filter needs to satisfy linearity, and out-of-channel rejection requirements as specified by UWB transmission. Due to the high-bandwidth requirements of UWB, the base-band filter is more susceptible to inter-modulation caused by amplifier non-linearities.
Discrete or integrated component passive filters having a pass-band of over 528 MHz are prohibitively large and lossy. That is the inductors, capacitors and resistor required to implement a 528 MHz pass-band filter are physically too large and lossy to be implemented or integrated in a UWB transceiver. Presently, active filters are difficult to design having 528 MHz pass-bands. Operational amplifiers of active filters need to have operational bandwidths that are substantially greater than the bandwidths required by the active filters. Therefore, for very large bandwidth active filters the bandwidth of the operational amplifier can be difficult to achieve.
It is desirable have a method and apparatus for providing a wide-bandwidth amplifier that is very linear and provides high out-of-channel rejection.